JP5866461B2 - Isotope modified optical fiber - Google Patents

Description

  The present invention relates generally to isotopically modified optical fibers, and in particular to silica fibers that are either Si-29 isotope atom depleted or enriched or Ge-73 isotope atom depleted or enriched.

Optical loss is a limiting factor in the design and construction of optical networks and links that typically include hundreds of kilometers of silica-based optical fibers. The optical loss of silica fibers is due to two factors: (1) Rayleigh scattering, which is attenuated as a function of 1 / λ ⁴ where λ is the wavelength and shorter wavelengths are dominant and (2) It is mainly caused by infrared absorption by silica, where long wavelengths are dominant. Typical germania (GeO ₂₎ doped silica core fiber has a loss of 0.189db / km~0.200db / km at 1510Nm～1610nm.

  Attempts have been made to develop optical fibers with lower transmission loss utilizing isotopic modification in the fiber region. See U.S. Pat. Nos. 6,810,197 and 6,870,999. Loss improvement is limited to about 0.145 to 0.155 db / km, mainly by shifting the minimum optical loss wavelength to about 1670 nm and partially changing the refractive index dopant from germania to oxygen-17. However, the inventors may not have recognized the reason for the loss reduction based on the use of oxygen-17.

  The Si-29 isotope is almost all the source of silica refractive index variation from 1.0000, and the natural isotope ratio Oxygen-17 provides a slight increase at the normal (natural) level. Scientists have not recognized it. Similarly, such technologists recognize that Ge-73 isotope (a commonly used dopant) increases the refractive index of fused silica from 1.46 to about 1.47 at its natural isotope ratio. I did not. Also, it has not been recognized that the Si-29 dopant is responsible for the majority of Rayleigh scattering present in existing optical waveguides. Si-29 is not recognized as a dopant because it is a naturally occurring stable silicon isotope.

  Thus, a material having a refractive index of 1.005 is obtained when the Si-29 isotope ratio in silica is reduced to about 1/100 (from 4.67% atoms / atomic to 0.0467% atoms / atomic). Reducing to 1/33 would yield a material having a refractive index of 1.015. These two materials with a refractive index difference of 1.015-1.005 = 0.010 are in the proper range sufficient to become a new fiber cladding and core, respectively.

  Similarly, in US Pat. No. 6,490,399, the replacement of silicon-28 isotopes with silicon-30 has a similar effect of moving the intrinsic IR absorption line to the right of the graph. Yes. As a result, a new usable transmission area is opened. See FIG. 2 which shows a region labeled “B” at a wavelength of about 1610 to about 1710 nanometers for both replacement of Si-28 with Si-30 and replacement of O-16 with O-18.

  US Pat. No. 6,810,197, “Summary of the Invention” (column 1, line 58 to column 3, line 14) describes the possibility of increasing the distance between amplifiers from 125 kilometers to 156 kilometers. As such, it is stated that the number of amplification stations required for the transatlantic link will be reduced by 11 units. However, it is almost certain that this advantage is actually an illusion. Any practical link that carries 1610-1710 would be designed to utilize the 1510-1610 band. Also, isotope substitution will not support fiber transmission in most of the 1510-1610 nm band. The same amplifier station that amplifies the 1610-1710 band would also amplify the 1510-1610 band. Proper operation in the latter band will require maintaining the same 125 km inter-amplifier distance as is currently required. Thus, the only available improvement would be to increase the available bandwidth over which signals can be transmitted. In other words, the replacement of Si-28 with Si-30 and the replacement of O-16 with O-18 does not actually allow any savings due to waveguide loss reduction. Also, even if the bandwidth is increased (including the 1610-1710 region), it is probably only beneficial for links where wavelength division multiplexing (WDM) signals already occupy all of the 1510-1610 bandwidth. I will.

Similarly, reference to the patent abstract of JP-A-60-90845 in US Pat. No. 6,490,399 includes an absorption band (including 1400 nm) by replacing the existing —OH group by —OD group. ) Is described using a deuterium rinse of a porous SiO ₂ preform to shift to a much longer wavelength longer than 1710 nm. Nevertheless, in part, the continuous improvement of the Cl ₂ treatment described in US Pat. No. 3,933,454, column 7, lines 1-8, line 68, allowed fiber manufacturers to The technology is described as “high cost” since it has already been successful in reducing OH content.

However, this only means that the —400 absorption spectrum (see FIG. 2) at 1400 nm, in particular, is sufficiently low compared to the “Rayleigh scattering” minimum line (see FIG. 3). It seems that it is not useful. The present invention has the effect of greatly reducing the “Rayleigh scattering” minimum intensity by a large related amount by significantly reducing the Si-29 concentration to 1/50 to 1/100 or less (partially). Therefore, a deuterium (D ₂ ) rinse described in JP-A-60-90845 could provide further utility.

  Thus, in one embodiment of the present invention that reduces Si-29, it is likely that deuterium (D2) rinses and further predictions from Si-28 substitution with Si-30 and / or O-16 substitution with O-18 or both. Outside benefits will be gained. Completely making these modifications can result in an optical waveguide having a transmission bandwidth of at least 1230 nm to about 2000 nm with a loss of about 0.01 db / km or less so that no amplifier station is used or at most one amplifier station Can be used to achieve transatlantic transmission.

  This attempt shifted the line representing “IR absorption” to the right of these graphs (see FIGS. 4 and 5). This has the effect of slightly reducing the minimum absorption due to a slight reduction in the sum of “IR absorption”, “Rayleigh [scattering]” and “UV”, and slightly widening the obtained transmission bandwidth.

  However, the present invention works not only on “IR absorption” lines but also on “Rayleigh scattering” lines. See the long diagonal line in FIG. 10 labeled “Rayleigh scattering”.

  If the Si-29 scattering center amount is reduced to “1 / X”, the “Rayleigh scattering” line intensity will decrease within the range of “1 / X” to “1 / square root X”. Therefore, when the Si-29 concentration is reduced to 1/33, the attenuation based on the Rayleigh scattering effect will be reduced to 1/33 to 1 / square root 33 (about 5.9). This dramatically reduces the total attenuation at the 1310 nm band and even at wavelengths up to about 1650 nanometers.

  Of course, combining some of the features of US Pat. No. 6,810,197, ie replacing O-16 with O-18 in both the core and near-core cladding regions and the Si-29 isotope When the ratio is dramatically reduced to 1/100 (0.0467% Si-29 atoms / atom), the combined attenuation of these together significantly reduces the total attenuation due to signal transmission through the optical waveguide.

  The authors of US Pat. No. 6,810,197 have found that the majority of oxygen-16 that would normally be present in non-isotopically modified fibers is oxygen-18 and at least to provide useful advantages. I thought it was necessary to replace some O-17 isotopes at the same time. See, for example, claims 1, 3, 4, and 9 of US Pat. No. 6,810,197.

  In contrast, the present invention specifies the presence or absence of the O-17 isotope, but rather than overlaps with the claims of US Pat. No. 6,810,197 or other patents or applications. Is a sufficiently low ratio.

  Anyone familiar with fiber optic waveguide design techniques, ie, a fiber optic technologist, can serve as a single mode transmission medium or other multimode transmission medium for a given transmission wavelength and core diameter. It would be possible to define the refractive index difference required to function.

  The refractive index of fused silica can be adjusted from a natural isotope distribution value of about 1.46 to virtually any value up to 1.0000 depending on the Si-29 isotope ratio reduction achieved. Accordingly, the above examples where the refractive indices are 1.015 and 1.005 are illustrative and not limiting.

  US Pat. No. 6,128,928 describes the anti-free oxygen effect of small amounts of germanium oxide doping added to the cladding region or inner cladding region of an optical fiber. In that regard, however, the refraction of the Ge-73 isotope (the author of US Pat. No. 6,128,928 is not aware that it is the majority of the source of the refractive index increasing effect). The rate increase effect is a drawback. Instead, the inventor of the present invention instead only has germanium atoms (or Ge-73 isotope atoms) other than Ge-73 isotope atoms to obtain the same advantages as US Pat. No. 6,128,928 without increasing the refractive index The majority)) is identified. The author of US Pat. No. 6,128,928 did not clearly anticipate the possibility that a germanium oxide isotope modified sample could be used instead of the natural isotope sample.

  The inventor of the present invention received a physics course numbered “8.03” at MIT in the fall of 1977 and was familiar with the principles of optics and waveguides. (

  At the beginning of 2007, the inventor had the opportunity to read a 1979 book on very advanced technical aspects of optical fiber construction and use. In November / December 2008, the inventor made Corning Glass Works vs. Sumitomo Electric US. S. A. 671F. SuppF 1369 (S.D.N.Y. 1987) District Court case and 868F. I had the opportunity to read both of the Federal Circuit appeal cases of 2d1251 (Fed.Cir. 1989). This provided a very extensive discussion of the history of optical fiber research and details on its construction and design.

  The inventor also accidentally obtained a list of naturally occurring isotopes of each of approximately 256 elements in total. Silicon consists of about 92% Si-28, 4.67% Si-29, and 3.1% Si-30. Germanium is about 7.8% Ge-73. A given nuclide (isotope nucleus) has a property called “spin” (actually “electromagnetic spin”) when it has either an odd number of protons or an odd number of neutrons. Thus, of the silicon isotopes, only Si-29 (4.67% atom / atom) has "spin" and only Ge-73 (7.8% atom / atom) has "spin". It was.

  “Spin” can be thought of as a permanent fluctuation caused by the fact that a single unpaired nucleon exists. This causes vibration of the (positively charged) nucleus, which behaves like a small bar magnet. This spin can be used for nuclear magnetic resonance analysis (most commonly hydrogen-1 atoms are used) and magnetic resonance imaging. Isotopes may also be used as “tracers” to track chemical reaction mechanisms.

  By reading the Corning case, the inventor found that the addition of about 8% (weight / weight) germania (GeO2) to silica (SiO2) reduced the refractive index of pure silica (1.4584) to about 1.466. Knew that it has the effect of raising. However, the present inventor was wondering why this was the case. The inventor has noticed the following. Since the silicon atom contained only 4.67% spin and the exchange germanium atom was 7.8% Ge-73, even the material had a refractive index of air or a refractive index of vacuum (1. The inventor thought that the underlying reason for having a refractive index greater than 000) is the presence of electromagnetic spin-containing atoms. It turns out that the inventor was correct. Even then, the inventor found that the inventor did not know if a given Ge-73 atom had a greater effect on the refractive index than the Si-29 atom overall, That was a question that the inventor could not answer at that time.

However, after realizing that Si-29 could be the underlying reason that silica has a refractive index greater than 1.000, several ideas were led in turn.
1. If Si-29 is added to silica instead of adding GeO2 to silica, the refractive index can be increased more than the refractive index of the cladding region.
2. If the Si-29 isotope atomic ratio in the cladding region is reduced rather than increased than in the core, it is possible to generate the refractive index difference necessary to make a functional optical waveguide.

  Both of these ideas are interesting, but will only provide a slight increase in benefits to the optical fiber manufacturing industry. Either idea will reduce light loss slightly over germania-doped optical fibers, but in either case, the rate factor will be maintained near 68% of c typical of existing optical fibers.

  The big question was how low the refractive index of the core and cladding could still function as a waveguide. As far as is known, the only limitation was that it was impossible to reduce the refractive index of the cladding material to a value of 1.0000, the same value as vacuum. Also, with such a cladding, the core will probably have to have a refractive index that is about 0.008 greater. Therefore it would be 1.0080.

  The resulting fiber will have a 99.2% rate factor of 1 / 1.08 or c. The inventor has realized that it would be very beneficial to optical fiber users if the signal could be accelerated to near 0.99 from an existing rate factor of 0.68. The inventor was unaware of the present invention of an optical fiber having a rate factor of 98-99% of c.

  But this was not surprising. This is because there is little need for isotopes of various elements and only a few attempts to separate the isotopes of the same element in the scientific industry are required.

  In the chemical field, tracer (stable) isotope tagged chemicals are sometimes used to analyze chemical reactions.

  In the early 2000s, three patents on the subject of stable isotope enhancement were granted. One was the Deutsche Telekom patent and the second was the Corning patent. However, the isotope ratios discussed for modification were only Si-16 to Si-30 or O-16 to O-18 and O-16 to O-17 within a smaller range. Only Si-29 was not considered.

A mechanism for the production of the necessary isotopically modified precursors (SiCl4, silicon tetrachloride) already exists. See "Silicon Kilogram Project" (Google "Silicon Kilogram Sphere"). They separated a silicon-containing precursor (probably either silane (SiH ₄ ) or silicon tetrafluoride (SiF ₄ )) in a Russian gas centrifuge and then converted it into single crystal silicon Converted. Instead, the present invention requires a silane or silicon tetrafluoride converted to SiCl4 that can be used directly as an input to the same type of optical fiber manufacturing process that Corning patented in 1976. To do.

  The development of optically transmissible materials and waveguides with significantly reduced refractive index has led to significant improvements in the optical technology field, meeting the long-standing demands of optical engineers.

The present invention is an isotope modification of silica (SiO ₂ ) having any refractive index below the natural value of 1.4584. This means that natural isotope ratio silica transmits light at a rate of c (1 / 1.4584). Where c is defined as the speed of light in vacuum. (By definition, the vacuum has a refractive index of exactly 1.000.) The speed of light in the vacuum is about 299,700 kilometers / second. Light travels through the air at about 0.999c. The graph shown in FIG. 1 is an excerpt from the 1989 issue of Encyclopedia Britannica, Macropedia, Volume 23, pages 665-666. The thinnest and darkest areas shown correspond to the optical glass that was available in 1880. It can be seen that known glasses having a refractive index of less than about 1.45 were not available in 1880. By 1934, the technology has progressed to the point of including glass with a refractive index as low as 1.40 (see the unshaded area labeled “Regular Optics”).

  The rest of the graph (thin tinted part) shows various types of glass “developed after 1934”. Of these, the “fluorophosphate” glass and the “fluoride” glass include a region having a refractive index of about 1.32. The reason why currently available glasses do not have a refractive index much lower than 1.4584 is that they are generally made of natural isotope ratio silica. In other words, the amount of Si-29 they contain is 4.67% (atoms / atom) of all natural silicon atoms. The inventor has found that the fact that the refractive index of silica is greater than 1.000 is almost entirely due to Si-29 (and much smaller proportions of O-17). Scientists do not understand this because they do not substantially see isotope ratio modifying materials. The silica they see always has a Si-29 ratio of 4.67% (atoms / atom). If it has an isotope ratio of 0.20% Si-29 atoms / atom, it is possible to produce silica having a refractive index of 1.02. If it has an isotope ratio of 0.10% Si-29 atoms / atom, it is possible to produce silica having a refractive index of 1.01, and the same applies to other cases. The effect was not exactly linear and these values were chosen for illustration purposes.

More particularly, the present invention relates to an optical waveguide comprising silica in which the silicon isotope Si-29 is present in various isotope ratios, which are typically highly depleted. When the Si-29 isotope ratio is dramatically reduced from the 4.67% (atom / atom) normally found in nature to about 1/50 (about 0.093% Si-29 isotope ratio), about 1 A fused silica with a refractive index of .010 will be obtained. This is in contrast to the 1.46 index of refraction present in fused silica with a natural isotope ratio. It is an object of the present invention to provide an optical waveguide with improved waveguide performance, including:
1. A signal rate factor that can be set to a value far exceeding the value of 0.67 (1 / 1.46 = 0.67) normally associated with silica having a refractive index of 1.46. This rate factor should be adjustable to at least 0.995, which means that the optical signal passes through the core region at a rate of 99.5% of c. Light travels in pure water at about 0.750c. Light travels in normal glass at about 66% of c. Thus, the data signal could move about 1.5 times faster than in a conventional prior art optical fiber.
2. A very large reduction in light loss from the 0.191 to 0.200 db / km normally found in germania-doped silica fibers and from the 0.160 db / km typically found in undoped core silica fibers. This reduction will be at least 1/5. Also, adding all the isotopic modifications will probably be much smaller than 1/50. When the latter value is achieved, and therefore when a loss value of 0.0032 db / km is achieved, the fiber signal is traversed across the Atlantic with or without intermediate re-amplification. It is possible to transmit. This reduction in Rayleigh scattering will span most of the 500 nm to 1650 nm band.
3. A significant reduction in chromatic dispersion and pulse broadening corresponds to a reduction in light loss, including most of the visible wavelengths from 400 to 700 nm, and most of the infrared wavelengths from 700 to 1650 nm.

In one embodiment, reducing the cladding refractive index to about 1.005 and the core refractive index of 1.015 would result in a rate factor of about 0.985. This means that the data signal travels at a rate of about 98.5% of the speed of light traveling in the vacuum. In this particular embodiment, the refractive index difference between the core and the cladding is achieved by at least the following four mechanisms.
1. The Si-29 isotope ratio of the silica in the core region is reduced to about 4.67% / 30, while the Si-29 isotope ratio of the cladding region is changed to about 4.67% / 100.
2. While reducing the Si-29 isotope ratio in both the core and cladding regions to about 4.67% / 100, add some Ge-73 isotopes (or higher ratios of natural isotope germania) To increase the refractive index to 1.015.
3. Reducing the Si-29 isotope ratio in both the core region and the cladding region to about 4.67% / 100 while simultaneously increasing the refractive index of the core to a level sufficient to maintain proper waveguide action A ratio of oxygen-17 isotope atoms greater than the 0.038% ratio found in nature is added.
4). Sufficient to raise the refractive index of the core to a level sufficient to maintain proper waveguide action while simultaneously reducing the Si-29 isotope ratio in both the core region and the cladding region to about 4.67% To some extent, both oxygen-17 and germanium-73 isotopes (or both germanium-73 containing both an oxygen-17 isotope atom and a significant isotope ratio of germanium-73) are added in core region quantities. .

  In other embodiments, the refractive index setpoints for the core and cladding regions are set to different values, but the difference maintains the relationship that functions to perform the operation of the waveguide. They can be set, for example, to a core refractive index of 1.04 and a cladding refractive index of 1.03.

  This selection alleviates the need to purify isotope samples of precursor material. The core region need only be made of silicon atoms with Si-29 content reduced to 1/12 of 4.67% atoms / atom found in natural samples, while the cladding The region need only be made of silicon atoms with a Si-29 content reduced to 4.17% atoms / atom of 1/17 of Si-29 isotope atoms.

In still other embodiments, both the core region and the cladding region are substantially all, with the usual ratio of Ge-73 isotope atoms being 1/100 and 1/300, respectively (7.8 similar to item 1 above). % / 100 and 7.8% / 300 atoms / atom) are constructed from germania (GeO ₂ ) that has been isotopically modified to reduce it. Similarly, in other embodiments, the core region and the cladding region are both substantially entirely isotopically modified to reduce the normal ratio of Ge-73 to 1/300 (7.8% / 300). However, the refractive index of the core is increased by adding a small amount of doping of Si-29 atoms or O-17 isotope atoms or both.

  In other embodiments, the core region is constructed to be directly surrounded by the inner cladding region and then surrounded by the outer cladding region to reduce the amount of isotope modifying material that must be utilized. And the material utilized in the outer cladding region can be depleted to a lesser extent of S9-29 isotopes. For example, the core can be set to a refractive index of 1.015, the inner cladding can be set to a refractive index of 1.005, and the outer cladding can be a natural isotope ratio found in samples on Earth. Si-29 that is the same or closer to the ratio of 4.67% atom / atom (relative to Si-29) or 7.8% atom / atom (relative to Ge-73) of these species found in (Or alternatively, Ge-73) isotope ratios. This construction method will tend to minimize the cost of the materials utilized. However, with this technique, the diameter of the inner / outer cladding boundary is such that light exceeding an acceptable ratio does not “leak” into the outer cladding region to increase the total attenuation of the fiber. Note that it must be sufficiently larger than the diameter of the core / inner cladding boundary. Those skilled in the field of optical fiber science and technology have mathematically predicted that the outer diameter of the inner cladding region is larger than the diameter of the core region enough to reduce the loss to an acceptable level, and experimentally It would be possible to check individually.

Source of isotope modifying material Silica is derived from a silicon-containing precursor depleted of Si-29 isotope atoms. These silicon-containing precursors can be of at least the following three types.
1) The isotope ratio of Si-28 isotope atoms is enhanced to about 99.5% atom / atom and the Si-30 isotope atoms are depleted to a very small or negligible amount. Such an isotope distribution can be expected from gas centrifuge effluents that select light molecules SiF ₄ or SiH ₄ .
2) The isotope ratio of Si-30 isotope atoms is enhanced to about 90% atoms / atom, and Si-28 isotope atoms are depleted to 10% or less. This will also be the output of a gas centrifuge that selects heavy molecules.
3) Although the isotope ratio of the Si-29 isotope atom is depleted from the natural ratio of 4.67% atom / atom, the relative ratio of the isotope atoms of Si-28 and Si-30 is greatly increased otherwise. There is no difference.

  In each of these examples, the Si-29 ratio is set to a value calculated to achieve a specific refractive index of the as-deposited silica material.

  In a typical preferred embodiment, using silica having an isotopic distribution of silicon atoms comprising about 0.1% Si-29 isotope atoms, the 90% + Si-30 isotope component of item 2 above and 99. The major difference from the 5% Si-28 isotope component will result in a wide passband for IR signal transmission at wavelengths above 1600 nm. The specific extent of the spread transmission spectrum and loss values cannot be easily predicted prior to fiber construction, but these additional usable frequencies can be compared to conventional optical waveguides, especially at losses well below 0.1 db / km. It will be understood that this has not been anticipated by waveguide technology. Also, these additional usable frequencies have not been provided or foreseen, and have been achieved by a transmission band from about 1400 nm that can be used equally due to ultra-low loss transmission. You will understand that too.

  Other objects and objects of the invention, as well as a more complete and more complete understanding thereof, will be achieved by referring to the accompanying drawings and by examining the following description of the best mode for carrying out the invention. sell.

FIG. 1 is a graph of refractive index n versus convergence ν for a series of optical glasses. Glass in Modern World by F.M. J. et al. Terence Maloney, 1968, Doubleday & Company, Inc. Excerpt from FIG. 2 is a reproduction of FIG. 1 of WO2003 / 0002834 pamphlet. FIG. 3 is a reproduction of FIG. 1 of US Pat. No. 6,490,399. FIG. 4 is a reproduction of FIG. 4 of US Pat. No. 6,810,197. FIG. 5 is a reproduction of FIG. 5 of US Pat. No. 6,810,197. FIG. 6 is a reproduction of FIG. 9 of US Pat. No. 6,810,197. FIG. 7 is a reproduction of FIG. 12 of US Pat. No. 6,810,197. FIG. 8 is a reproduction of FIG. 10 of US Pat. No. 6,810,197. FIG. 9 is a reproduction of FIG. 11 of US Pat. No. 6,810,197. FIG. 10 is a reproduction of FIG. 2 of US Pat. No. 6,810,197.

Advantages of the present invention By reducing the Si-29 content from natural 4.67% atoms / atom to about 0.01% and even lower, glass materials with a refractive index as low as 1.001 are available. Thus, the refractive index of the core of the waveguide can be about 1.001 to 1.002, so the “rate factor” of the signal transmitted through the fiber is at least (1 / 1.1. 001) or c can be as high as 99.9%.

  Existing fiber optic cables typically utilize waveguides that operate at a rate factor of about (1 / 1.47) or 68% of “c”. The signal can be transmitted over a distance of about 6,000 kilometers, the cable length between New York and London, with a one-way delay within about 36 milliseconds. Even with the currently proposed route designed to be more linear and more direct, the cable distance of 5000 and the one-way delay of 30 milliseconds are the smallest that current technology can provide It is.

  However, changing this fiber to a fiber with a rate factor of 99.5% instead of the typical 68% value so far, about 2/3 of 36 milliseconds or 24 milliseconds in one direction on the longer path. Delay is obtained. Using that higher speed fiber with a shorter path expected to have a one-way delay of 30 milliseconds when using a normal cable, two-thirds of 30 milliseconds, or a one-way delay of 20 milliseconds. Will be obtained.

  This type of signal delay difference is extremely important for real-time interactive video, server response, database lookup, Internet games, and low latency telephony in general. It also allows the database and other servers to be located further away from the user with the same delay.

  Financial markets such as stock exchanges will be particularly affected. With an additional delay of a few milliseconds in each direction, large stock trading companies can cost tens of millions of dollars each month. When the delay between New York and London is reduced to 2/3, or between New York and Los Angeles from 36 milliseconds to 24 or even 20 milliseconds, not just one country but eventually the whole world It will be tied more closely.

  Internet games are another use. Currently, for example, two users located in New York and Sydney, Australia, are locked with (taste) digital combat, and their computers are only known 100 milliseconds after the other party has done. These delays appear to be small, but are quite noticeable and have a substantial impact on the game flow. If the one-way link delay is reduced to 2/3 from 100 milliseconds to 67 milliseconds, the minimum theoretically possible delay will be provided.

Advantages on optical loss It has long been recognized that the minimum optical loss of a pure silica core waveguide at a minimum loss of about 1560 nm is 0.151 db / km. This was slightly changed by replacing Si-28 with Si-30 and O-16 with O-18. However, improvements to less than 0.10 db / km still seem difficult to achieve and are considered expensive.

  The present invention reduces optical loss to 1/10, and in some cases 1/100 or less, by reducing Si-29 to 1/50, 1/100, or less. This makes it possible to achieve a repeater spacing of 5000 kilometers or more.

Advantages of increased optical bandwidth According to the present invention, the current optical bandwidth of 1510 to 1610 nanometers is increased to at least 1450 nm to 1800 nm, and in some cases from 1230 nm to 2000. To fully utilize some of these wavelengths, production of suitable transmitter lasers and detectors is awaited, but most of this new transmission area should be available almost immediately. In either case, this new capacity fiber can be installed immediately, can operate in the traditional 1510-1610 band, and the frequency band can be expanded when receivers and transmitters become available. is there.

  However, if an amplifier matched to the fiber that amplifies the additional bandwidth (if present) is not used, as in US Pat. No. 6,810,197, 1510 to include a band of 1610-1710 nm, for example. Simply increasing the transmission bandwidth of the ˜1610 nm optical fiber is of little value. Erbium-based fiber amplifiers amplify in the bandwidth region of about 1520 to 1565 nm and make this the main transmission region. While it would be possible for each amplifier to detect and retransmit such a signal, this is expensive and renders additional bandwidth worthless. It would be cheaper to simply install additional fibers to achieve greater capacity.

  Instead, not only is this bandwidth available, but if it is available with a loss of about 0.01-0.02 db / km, a wider bandwidth is available, and any fiber amplifier can be used at all. Not used (or use at most one detection and retransmission amplifier in the middle of the Atlantic).

  The bandwidth available by utilizing the present invention is about 320 nm, about 1430-1750, using the normal isotope distribution of Si-28 versus Si-30 and O-16 versus O-18. It is seven times 45 nm of the 1520 to 1565 nm band. By utilizing almost all Si-30 or almost all O-18, the available bandwidth increases to 1430-2000 nm or 570 nm, which is about 13 times the 1520-1565 nm band.

Dramatically reduced material-derived dispersion factor A significant reduction in the Si-29 isotope atomic ratio in the waveguide material will correspondingly significantly reduce the total dispersion of the optical waveguide during manufacture. See FIGS. 6 and 7. The dispersive part (see FIG. 8) that can be attributed to the waveguide itself will probably remain the same. The profile variance can also be selected to offset any residual total variance that may remain after the end of other isotope modification processes. Those familiar with fiber optic waveguide design techniques will be able to define various permutations of core-to-cladding to achieve the desired level of dispersion.

  The present invention significantly reduces the Si-29 isotope ratio in the core and cladding regions (approximately 1/3 of the natural 4.67% atom / atom of all silicon atoms present in the Si-29 ratio). In combination with “O-8 core / O-16 clad” inferred from FIG. 9 (profile D), “material D [dispersion] (core) inferred from FIG. ”And a redesigned optical waveguide that results in a slight change (if any) in the“ waveguide D [dispersion] ”curve inferred from the curve of FIG.

  In other words, the monotonically increasing line of line 4 of FIG. 9 will partially compensate for the monotonically decreasing line of lines 1 to 4 of FIG. The additive residual of these values can be combined with a Si-29 decreasing curve similar to line 4 in FIG. This combination can be expected to have a much gentler slope than that of US Pat. No. 6,810,197.

  The wisely selected total dispersion similar to “total D [dispersion]” in FIG. 7 is a linear sum of “material dispersion”, “waveguide D [dispersion]” and “profile D [dispersion]”. Will. This is also a very significant decrease from the value of about 20 ps / nm / km at a wavelength of 1.6 microns with the normal isotope “O-16 core / O-16 clad” shown in FIG. The value may be less than 0.0 ps / nm / km.

  Fiber optic waveguide technologists have long been accustomed to the need and use of dispersion compensating fibers (DCF). The purpose of these fibers, used in relatively short lengths (compared to hundreds or thousands of kilometers present in typical optical waveguide links), is the arrival of various wavelength portions of a given optical signal Dealing with changes in time, that is, canceling out the effects and completely or partially offsetting them. Their use can be important in order to be able to achieve the maximum bit rate (technically the symbol rate) that can be carried by a given actual data link. The reason is that the arrival time of movement of the optical signal constituting a given bit tends to become blurred with time due to dispersion.

  For example, a symbol rate of 40 Gbit / second (40 billion bits / second) means that (1 / 40,000,000,000) bit time = 25 picoseconds when there is one bit in each optical signal symbol. To do. This rate of 40 Gbit / s is the fastest commercially available data transfer rate available on the most recently installed (or upgraded) data link. However, if a bit (symbol) spreads over time, for example over 50 picoseconds, it would be useless to have a photodetector that can detect a minimum signal time of 25 picoseconds. According to Fourier's law, the optical wavelength bandwidth of a 40 Gbit / s signal is a minimum of about 0.3 nanometers, so that a conventional uncompensated fiber with a dispersion of 20 ps / nm / km is about 4 kilometers. After a fiber length of 25 picoseconds, blurring due to dispersion occurs in a time of 25 picoseconds. It can therefore be seen that it is essential to compensate for this dispersion in order to be able to maintain 40 Gbit / s even with short distance fibers.

  The majority of fiber optic dispersion is currently compensated using dispersion compensation products, but any such compensation tends to be limited to less than 100% completeness. Therefore, the better the main fiber (the lower its baseline dispersion), the better the final compensation optical link dispersion. The possibility of the present invention to reduce the natural uncompensated fiber dispersion to 1/10 or less offers the possibility of a similar improved signal dispersion during compensation.

The present invention may utilize the technology of US Pat. No. 4,435,040 Optical waveguides constructed using the present invention may also be made with US Pat. No. 4,435,040 with particular care and modifications. It is expected that the double clad process described in the specification can be used. First, it should be noted that in the prior art waveguides, the core and cladding have a refractive index very close to 1.46 of natural isotope-distributed silica. The physical wavelength of the optical signal in such a waveguide is, for example, 1510 nanometers divided by 1.46, or approximately 1050 nanometers. In contrast, for a waveguide with a refractive index of about 1.01, the physical wavelength of the waveguide is 1510 nanometers / 1.01, or about 1495 nanometers. Since the behavior of the wave in the waveguide is based on the size of the waveguide relative to the light wave, the dimensions of the waveguide elements, such as the core and cladding, are about 1.46 / 1.01 of all other equal technology fibers. The size can be expected to be 1/1 / 1.45.

  For example, US Pat. No. 4,435,040 specifies an effective core diameter greater than 2 × 4 microns or 8 microns, which is 8 microns × 1: 45 or about 11.6 microns. Would be interpreted as a core diameter of Similarly, U.S. Pat. No. 4,435,040 specifies a difference of about 0.5 to 0.8 times between the core radius and the inner cladding radius. When calculated for 11.6 microns, the OD of the inner cladding is approximately 23.2 microns to 14.5 microns.

  Also, in U.S. Pat. No. 4,435,040, the thickness of the outer cladding region is about 6-8 times greater than the core radius, i.e. (6-8) x (5.8 microns), i.e. 34 It is expected that the outer cladding region OD should be 11.6 + 2 (34.8-46.6), ie 81.2-104.8. Will be micron. Nevertheless, the outside of the outer cladding region can have other cladding regions, possibly having a refractive index equal to that of normal silica, ie 1.46.

  Another note is that many patents, such as US Pat. No. 4,435,040, expect the percent change in refractive index of the material to be close to, for example, the value of natural isotope silica, or 1.46. This is a point that it is “0.1% to 0.6%” of a possible value. This is interpreted as a change of 0.1% x 1.46 or a difference of 0.00146 to a 0.6% of 1.46 or about 0.00876.

  However, to significantly reduce the Si-29 content, for example, to reduce it to about 1/100 of the natural 4.67% atom / atom of Si-29, therefore, a refractive index of about 1.005. Thus, when the silica material is isotope modified, the value (1.005) cannot be reduced by 0.00876. The refractive index of the actual uniform material cannot be less than the refractive index of the vacuum, i.e. 1.000. Therefore, the percentage change in refractive index (for example, “0.1% to 0.6%”) cannot be used as it is, which reflects the numerical difference in refractive index that exceeds the intended refractive index of 1.000. Those skilled in the art of optical waveguide design will apply the principles originally intended for refractive index materials near 1.46 to new materials with a refractive index very close to 1.00. We can expect to be able to interpret it as successfully as possible.

Refractive Index of Fused Silica as a Function of Isotope Ratio of Si-29 Isotope Atoms As noted above, the refractive index of silica is the normal (naturally found) value of the silicon-29 isotope percentage. It will change as it changes from 4.67% atom / atom. To calculate the refractive index of silica for a given ratio of Si-29, the following equation is used:
Refractive index (silica) = SQRT (1+ (1.131 ((Si-29 atoms / atomic percent) /4.67%)))

  The difference in refractive index between fused silica having a Si-29 content of 1/40 of the natural value and fused silica having a Si-29 content of 1/100 of the natural value is 1.0140-1.0056 = 0.0084.

  This difference is approximately equal to the index difference utilized by a typical single mode optical waveguide. Thus, it contains a core region containing pure fused silica having a silicon isotope ratio of 0.117% (atom / atom) and pure fused silica having a silicon isotope ratio of 0.0467% (atom / atom). It is possible to construct an optical waveguide using the cladding region. Optical waveguide designers can control the refractive index of pure fused silica without adding any extraneous dopants, so that optical waveguide designers can control optical properties more powerful than existing ones. Will be apparent to those skilled in the art.

  The most obvious improvement that can be achieved is the construction of an optical waveguide utilizing a material having a core refractive index of 1.02. The resulting rate factor will be about (1 / 1.02) or 98% of c. A fiber of this characteristic will dramatically reduce the associated data latency during operation.

  Although not so obvious, the second improvement is that the Si-29 isotope atom itself corresponds to the dopant, and the optical loss is a function of Rayleigh scattering caused by the dopant atom, so the concentration of Si-29 atom is reduced. When reduced to 1/40 (from the above example), the optical loss can be reduced to 1/40 of the 0.19 decibel / km value typically found in germania-doped core silica clad optical fibers. With this magnitude of optical loss, perhaps up to 0.005 db / km, the need for an optical amplifier can be substantially avoided except for the longest fiber link.

  If the inherent loss of silica is so greatly reduced, manufacturing defects and constraints that must be corrected can be eliminated. Also, connection loss reduction research will be more urgent. A connection of 0.2 dB loss may appear to be appropriate when equivalent to 1.0 km fiber loss (0.19 db / km), but 40 km fiber loss (40 × 0.005 db) / Km) would be totally unacceptable.

  The third improvement is that the chromatic dispersion of the silica itself can be dramatically reduced to about 1/40, possibly by reducing the Si-29 isotope content described in the above examples to 1/40. Would be very expensive. Since total waveguide dispersion is a function of the sum of dispersions caused not only by the material but also by the shape of the waveguide itself, it is more difficult to predict the overall improvement that can be achieved, but the magnitude of the total dispersion Can be reduced to 1/10. With such improvements, higher symbol rates (often equal to the bit rate) are possible and the need for complex dispersion compensation currently in use can be dramatically reduced.

  A fourth improvement is the useable light, especially when the total light loss is similarly reduced to 1/40, corresponding to reducing the Si-29 ratio to 1/40 in the example described above. The frequency range will be greatly expanded. Currently, the longest distance data link is limited to wavelengths near 1540 nanometers, but the usable area is limited near 950 nm and 1,400 nm, possibly extending to 500-2000 nanometers Yes. Auxiliary optics and electronics required to support such wider bandwidths must be available, but a given installed fiber will utilize these new wavelength regions For later use.

  1. The optical waveguide includes a cladding layer made of high-purity optical glass mainly made of silica and / or germania, and a core region made mainly of high-purity optical glass made of silica and / or germania. May be included. However, one or both of the glasses contains silicon atoms with silicon-29 isotope atoms less than 4.44% atoms / atom or germanium-73 isotope atoms less than 7.41% atoms / atom Containing a germanium atom, or both.

  Each percent can be 0.95 times the normal Si-29 and Ge-73 isotope ratio found in samples of the earth on each element.

  When the waveguide is constructed of silica, at least 10% of the oxygen atoms in the core or cladding can each be oxygen-18.

  2. The optical waveguide includes a cladding layer made of high-purity optical glass mainly made of silica and / or germania, and a core region made mainly of high-purity optical glass made of silica and / or germania. May be included. However, at least 50 mole percent of the oxygen in the core and / or at least 50 percent of the oxygen in the cladding is oxygen-18. In addition, however, the core region and / or the cladding region may contain oxygen-17 isotopes in a proportion of less than 5 atomic percent of the amount of oxygen-18 isotopes.

  3. The optical waveguide includes a cladding layer made of high-purity optical glass mainly made of silica and / or germania, and a core region made mainly of high-purity optical glass made of silica and / or germania. May be included. However, at least 70 atomic percent of the core and / or cladding oxygen is oxygen-18. In addition, however, the amount of oxygen-17 atoms is less than 5 atomic percent of the total oxygen atom content.

  4). Any of the optical waveguides of Examples 1 and 2, further comprising a dopant in the core and / or cladding. However, the dopant in the core need not be the same as the dopant in the cladding, and they need not be the same concentration or present at the same concentration in the core and in the cladding. The dopant can be a natural isotope ratio germanium, any unnatural isotopic distribution germanium, or a Si-29 isotope, or phosphorus, or combinations thereof.

5. In all the optical waveguides of Examples 1, 2, and 3, the volume percentage of the region containing SiO ₂ depleted of Si-29 or the volume percent of the region containing GeO ₂ depleted of Ge-73 was 50%. Can be less.

  6). In the optical waveguide of Example 1, at least 70 atomic percent of oxygen in the core can be oxygen-18, or at least 70 atomic percent of oxygen in the cladding region proximate to the core is oxygen-18. And the amount of oxygen-17 can each be less than 5 atomic percent of the total oxygen atom content in those regions.

  7). In any of the optical waveguides according to the present invention, the core may have a constant or gradient refractive index.

  8). In any of the optical waveguides according to the present invention, the fiber can be surrounded by an outer layer made of glass or plastic.

  9. In any of the optical waveguides according to the present invention, the glass material is pure or has an isotope ratio of Ge-73 isotope reduced to at most 7.2 atoms in one or both of the core region and the cladding region. Can include doped germania glass.

  10. In any of the optical waveguides according to the present invention, in the core region and / or the cladding region, the O-18 isotope ratio is increased to at least 10 atomic percent and at most 100% of the total oxygen isotope atoms present. It can be made.

  11. In any of the optical waveguides according to the present invention, the Si-29 isotope is present as a dopant in the core and / or the cladding.

  12 In any of the optical waveguides according to the present invention, the O-17 isotope ratio can exceed the natural O0-17 isotope ratio of 0.038 atomic% found on the earth.

  13. In any of the optical waveguides according to the present invention, O-17 can be depleted in the core or cladding from the natural O-17 isotope ratio of 0.038 atomic% found on the earth. In addition, Si-29 isotopes can be present in the core or cladding or both in natural or non-natural ratios.

  14 In the optical waveguide according to the present invention, the refractive index difference between the core region and the cladding region is completely or partially due to the difference in the isotope ratio of Si-29 in silicon, or Ge-73 in germanium. It can be designed to remain above 0.001 atomic% due to the difference in isotope ratio.

  15. In any of the optical waveguides according to the present invention, as described in the patent abstract of JP-A-60-90845, -OH can be reduced by using deuterium rinsing.

  16. In any optical waveguide according to the present invention, the refractive index of the cladding can be reduced by using a fluorine compound. In addition, the isotope ratio of Si-30 or O-18 or both can be greater than that of natural in the core and / or cladding.

  17. The present invention also includes less than 4.44 atomic percent Si-29 atoms or less than 7.41 atomic percent Ge-73 atoms or greater than 4.90 atomic percent Si-29 atoms or greater than 8.18 atomic percent Ge-. It is a light-transmitting material made primarily of silica and / or germania that has been isotopically modified to contain 73 atoms.

  18. In any of the optical waveguides according to the present invention, the cladding or cladding layer can be doped with an isotopically modified sample of germanium atoms, or the innermost cladding layer can be an Ge--isotope distribution of germanium atoms present. It can be modified to reduce the 73 isotope to at most 7.2 atomic percent. Preferably, the amount of germanium dioxide is from 0.005% to 1% by weight, more preferably from about 0.1% to about 0.5%, most preferably from about 0.1% to about 0.3%. Within the weight percent range.

  The invention has been described with reference to specific embodiments. However, it will be apparent to one skilled in the art to which this invention pertains that other modifications and enhancements may be made without departing from the spirit and scope of the following claims.

Claims (24)

a) a cladding layer of a first optical glass, wherein the first optical glass comprises one of silica, germania, and a mixture of silica and germania, the first optical glass comprising: A first optical glass cladding layer having a refractive index of:
b) a core region of a second optical glass, wherein the second optical glass comprises one of germania and a mixture of silica and germania, wherein the second optical glass has a second refractive index An optical waveguide comprising a core region of a second optical glass having
The atomic percent of Si-29 relative to all other Si isotopes in the silica is
One of greater than 0 and less than 4.44, and greater than 4.90 and less than or equal to 100,
The atomic percent of Ge-73 relative to all other Ge isotopes in the germania is
An optical waveguide characterized by being one of more than 0 and less than 7.41, and more than 8.18 and 100 or less. The waveguide of claim 1, wherein the atomic percentage of O-17 relative to all other O isotopes is one of silica, germania, and a mixture of silica and germania.
A waveguide characterized by being greater than 0 and less than 0.038, and greater than 0.038 and less than or equal to 100.   The waveguide according to claim 1, wherein the first refractive index is lower than the second refractive index.   2. The waveguide according to claim 1, wherein at least 10% of oxygen atoms in the silica are oxygen-18.   The waveguide of claim 1, wherein at least 50 mole percent of oxygen in the core region is oxygen-18, and less than 5 atomic percent of oxygen in the core region is oxygen-17. Waveguide.   The waveguide of claim 1, wherein at least 50 mole percent of oxygen in the cladding layer is oxygen-18, and less than 5 atomic percent of oxygen in the cladding layer is oxygen-17. A featured waveguide.   The waveguide of claim 1, wherein at least 70 atomic percent of oxygen in the core region is oxygen-18, and less than 5 atomic percent of oxygen in the core region is oxygen-17. Waveguide.   The waveguide of claim 1, wherein at least 70 atomic percent of oxygen in the cladding layer is oxygen-18, and less than 5 atomic percent of oxygen in the cladding layer is oxygen-17. A featured waveguide.   The optical waveguide according to claim 1, wherein the cladding layer further contains a dopant.   The optical waveguide according to claim 1, wherein the core region further includes a dopant.   11. The optical waveguide of claim 9 or 10, wherein the dopant is selected from the group consisting of germanium with a natural isotope distribution, germanium with a non-natural isotope distribution, silicon-29, phosphorus, silicon-29, and mixtures thereof. An optical waveguide characterized by being made.   The optical waveguide according to claim 1, wherein the volume percentage of the region containing silica containing Si-29 of less than 4.67 atomic percent is less than 50.   The optical waveguide according to claim 1, wherein the volume percentage of the region containing germania containing Ge-73 of less than 7.8 atomic percent is less than 50.   The optical waveguide according to claim 1, wherein the refractive index changes in a radial direction.   2. The optical waveguide according to claim 1, further comprising an outer layer surrounding the cladding layer.   16. The optical waveguide according to claim 15, wherein the outer layer is made of a material selected from the group including glass and plastic.   2. The optical waveguide according to claim 1, wherein a hydroxyl concentration in the first and second optical glasses is reduced as compared with a normal optical glass.   18. The optical waveguide according to claim 17, wherein the reduction of hydroxyl is achieved using deuterium rinsing.   2. The optical waveguide according to claim 1, wherein the first optical glass further contains a fluorine-containing compound, whereby the first refractive index is further reduced.   2. The optical waveguide according to claim 1, wherein the cladding layer further comprises 0.005 to 1% by weight of germanium dioxide.   2. The optical waveguide according to claim 1, wherein the cladding layer further comprises 0.1 to 0.5% by weight of germanium dioxide.   2. The optical waveguide according to claim 1, wherein the cladding layer further comprises 0.1 to 0.3% by weight of germanium dioxide. In a light-transmitting material containing germania or a mixture of silica and germania,
The atomic percent of Si-29 relative to all other Si isotopes in the silica is
One of greater than 0 and less than 4.44, and greater than 4.90 and less than or equal to 100,
The atomic percent of Ge-73 relative to all other Ge isotopes in the germania is
An optically transmissive material characterized by being one of more than 0 and less than 7.41, and more than 8.18 and 100 or less. 24. The light transmissive material of claim 23, wherein the atomic percent of O-17 relative to all other O isotopes is
An optical transmission material characterized by being one of more than 0 and less than 0.038, and more than 0.038 and 100 or less.

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